This invention relates generally to fluid drop ejectors and method of operation, and more particularly an array of fluid drop ejectors wherein the drop size, number of drops, speed of ejected drops and ejection rate are controllable.
Fluid drop ejectors have been developed for inkjet printing. Nozzles which allow the formation and control of small ink droplets permit high resolution printing resulting in sharp character and improved tonal resolution. Drop-on-demand inkjet printing heads are generally used for high resolution printers.
In general, drop-on-demand technology uses some type of pulse generator to form and eject drops. In one example, a chamber having a nozzle is fitted with a piezoelectric wall which is deformed when a voltage is applied. As a result, the fluid is forced out of the nozzle orifice and impinges directly on the associated printing surface. Another type of printer uses bubbles formed by heat pulses to force fluid out of the nozzle. The drops are separated from the ink supply when the bubbles collapse. In U.S. Pat. No. 5,828,394 there is described a fluid drop ejector which includes one wall having a thin elastic membrane with an orifice defining a nozzle and transducer elements responsive to electrical signals for deflecting the membrane to eject drops of fluid from the nozzle. The disclosed fluid drop ejector includes a matrix of closely spaced membranes and elements to provide for the ejection of a pattern of droplets. An improvement employing piezoelectric actuating transducers is disclosed in co-pending application Ser. No. 09/098,011 filed Jun. 15, 1998. The teaching of the ""394 patent and of the co-pending application are incorporated herein in their entirety by reference. In order to obtain high resolution, many closely spaced ejector elements are required. For high resolution, the elastic membranes are in the order of 100 microns in diameter. We have found that, due to the small size of the elastic membranes, the displacement of the membranes is, in some cases, insufficient to eject certain fluids and solid particles.
It is an object of the present invention to provide an improved droplet ejector.
It is another object of the present invention to provide an improved two-dimensional array droplet ejector.
The foregoing and other objects of the invention are achieved by a material ejector which includes a cylindrical reservoir with an elastic membrane closing one end, and bulk actuation for resonating the material in said reservoir to eject the material through an orifice in said membrane. The injector may include an array of membranes and a single bulk actuator or an array of bulk actuators. The membrane may include individual actuators.